Visitor comments: Comments about Replay Gain in Linux

I've written a script to automate adding replaygain tags to an entire music library. You can find it here: http://ubuntuforums.org/showthread.php?p=8376659#post8376659

Also, Quod Libet doesn't just support using replaygain tags. It also has an excellent plugin for *adding* them for all file types that it can play.

Newer versions of mp3gain can now also write id3v2 tags: they add the standard RVA2 tags, as well as mp3gain-specific MP3GAIN_ALBUM_MINMAX, MP3GAIN_MINMAX and MP3GAIN_UNDO. The command line option is "-s i".

Note that mp3gain changes more than just tags! It also adjusts the bulk volume level for each MP3 frame (a field in each frame's header). That is a lossless operation because the audio stream is not re-encoded. But you absolutely need the MP3GAIN_UNDO tag if you would like to revert that change.

I made some changes to also incorporate mp3 and vorbis scanning, and to do it as quietly as possible so it can be run via cron.

#!/bin/bash

# tag-flac-with-rg.sh
# Script created by Bobulous, October 2008.
# See www.bobulous.org.uk/misc/Replay-Gain-in-Linux.html
#
# Modified by Qsx/4011 to also tag mp3 and vorbis files
#
# This script takes as an argument a directory name,
# then uses metaflac to add Replay Gain tags (for album and
# track gain) to each FLAC, MP3, or Vorbis file in that directory.
#
# Use find (with -exec) to call this script on
# a directory structure containing FLAC files, so that this
# script is run on each directory in that structure. E.g.
# find ./music/flac -type d -exec ~/tag-all-with-rg.sh '{}' \;
#
# Or, better yet, try GNU Parallel to use multiple CPU cores
#
# See www.bobulous.org.uk/misc/Replay-Gain-in-Linux.html
#

# Error codes
ARGUMENT_NOT_DIRECTORY=1

# Check that the argument passed to this script is a directory.
# If it's not, then exit with an error code.
if [ ! -d "$1" ]
then
	echo "Arg "$1" is NOT a directory!"
	exit $ARGUMENT_NOT_DIRECTORY
fi

# Count the number of audio files in this directory.
flacnum=`ls "$1" | grep -c \\.flac`
mp3num=`ls "$1" | grep -c \\.mp3`
vorbisnum=`ls "$1" | grep -c \\.ogg`

# If no audio files are found in this directory,
# then exit without error.
test $flacnum -lt 1 && test $mp3num -lt 1 && test $vorbisnum -lt 1 && exit 0

# Run metaflac on the FLAC files in this directory.
test $flacnum -gt 0 && metaflac --add-replay-gain "$1"/*.flac

# Run mp3gain on the MP3 files in this directory.
test $mp3num -gt 0 && mp3gain -q -s i "$1"/*.mp3

# Run vorbisgain on the Vorbis files in this directory.
test $vorbisnum -gt 0 && vorbisgain -afqn "$1"/*.ogg

exit 0